Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 2, 2000
Publication Date: December 20, 2000
Citation: Kappes, S.M., Bennett, G.L., Keele, J.W., Echternkamp, S.E., Gregory, K.E., Thallman, R.M. 2000. Initial results of a genomic scans for ovulation rate in a cattle population selected for increased twinning rate. Journal of Animal Science. 78(12):3053-3059. Interpretive Summary: Genetic factors that affect reproduction are not well understood and identifying these factors could lead to substantial improvements in these traits, primarily by genetic selection but also with pharmaceuticals to enhance reproduction. The MARC twinning population is well suited to identify genes that influence ovulation rate and twinning rate. Genes that influence ovulation rate are likely to be involved in follicular recruitment and development, or ovulation. Genes that influence twinning rate and not ovulation rate are likely to be involved in fertilization, embryo survival, implantation or other components of conception. Current results strongly suggests that a gene(s) exists on chromosome 5 that affects ovulation rate in cattle. Identification of this gene(s) and other genes affecting ovulation rate and twinning rate will increase the basic understanding of the reproductive process and may also be used to improve reproductive efficiency in cattle.
Technical Abstract: A genomic scan was conducted with 273 markers on 181 sires from a cattle population that has been selected for increased twinning rate to identify chromosomal regions that influence ovulation rate. Criteria used for selecting markers were number of alleles, ease of scoring, and relative position within the linkage group. Markers were multiplexed or multiple loaded on a gel to reduce cost and labor requirements. This reduced the number of gels required for the genomic scan by 45% when compared to running each marker independently. The male animals selected for the genomic scan sired the majority of the population. A modified version of interval analysis was used in a granddaughter design to compare the effects of each allele within a sire for 10 different sire families. The midparent deviation of the son's estimated breeding value for ovulation rate was used as the phenotype. Forty-one potential peaks were identified with a nominal significance level </=.05. The 10 peaks with the highest significance levels (P<.02) were selected for further analysis. Markers were run across daughters of the sire for each of the 10 peaks. One peak (BTA5, relative position 40 cM) was found to be nominally significant in the daughters. The nominal significance levels were .01 for the sons (n=32) and .02 for the daughters (n=94) of the 784403 sire. A combined genome-wide significance value (P=.07) was calculated that accounted for the 10 analyses with sons and the 10 analyses with daughters and it strongly suggests that this region contains a gene(s) that is involved in the follicular recruitment and/or development process.